We now keep a separate queue of empty ChunkedBlocks in each allocator.
The underlying memory for each block is mprotect'ed with PROT_NONE to
provoke crashes on use-after-free.
This is not going to catch *all* use-after-frees, but if it catches
some, that's still pretty nice. :^)
The malloc memory region names are now updated to reflect their reuse
status: "malloc: ChunkedBlock(size) (free/reused)"
This one is a bit mysterious. I can't find any authoritative answer on what
the correct behavior is, but it seems reasonable to me that free() doesn't
step on errno, since it returns "void" and thus the caller won't know to
inspect errno anyway.
